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|
| function quickselect(arr, k, left, right, compare) {
| quickselectStep(arr, k, left || 0, right || (arr.length - 1), compare || defaultCompare);
| };
|
| function quickselectStep(arr, k, left, right, compare) {
|
| while (right > left) {
| if (right - left > 600) {
| var n = right - left + 1;
| var m = k - left + 1;
| var z = Math.log(n);
| var s = 0.5 * Math.exp(2 * z / 3);
| var sd = 0.5 * Math.sqrt(z * s * (n - s) / n) * (m - n / 2 < 0 ? -1 : 1);
| var newLeft = Math.max(left, Math.floor(k - m * s / n + sd));
| var newRight = Math.min(right, Math.floor(k + (n - m) * s / n + sd));
| quickselectStep(arr, k, newLeft, newRight, compare);
| }
|
| var t = arr[k];
| var i = left;
| var j = right;
|
| swap(arr, left, k);
| if (compare(arr[right], t) > 0) swap(arr, left, right);
|
| while (i < j) {
| swap(arr, i, j);
| i++;
| j--;
| while (compare(arr[i], t) < 0) i++;
| while (compare(arr[j], t) > 0) j--;
| }
|
| if (compare(arr[left], t) === 0) swap(arr, left, j);
| else {
| j++;
| swap(arr, j, right);
| }
|
| if (j <= k) left = j + 1;
| if (k <= j) right = j - 1;
| }
| }
|
| function swap(arr, i, j) {
| var tmp = arr[i];
| arr[i] = arr[j];
| arr[j] = tmp;
| }
|
| function defaultCompare(a, b) {
| return a < b ? -1 : a > b ? 1 : 0;
| }
|
| export default quickselect;
|
|
